only use the ip_families option **when explicitly passed by the user**; the client may have local network IPv6 connectivity and may prefer connecting to IPv6 in such situations

DNS filtering is already ensured, as the resolvers list is for support networks only

this was making the parser initialize in some situations, which would break the look as it'd put bytes in the buffer for http/2

instead of relying on sniffing exception details which may have been there or not. this way it should have the same level of accuracy as before and require a less janky API

Fixes https://github.com/HoneyryderChuck/httpx/issues/106